Resource allocation for beam failure recovery procedure

ABSTRACT

The present disclosure relates to a mobile terminal, a base station, an operating method for a mobile terminal and an operating method for a base station. The mobile terminal is for communicating in a mobile communication system with a base station using at least one of a plurality of downlink beams and at least one of a plurality of uplink beams, each of the downlink and uplink beams having different directivities and/or coverage, comprising: which, in operation, receives for a beam failure recovery, BFR, procedure an allocation of dedicated uplink radio resources for transmitting a beam failure recovery signal, a processor which, in operation, detects a downlink beam failure event and, in response thereto, initiates the beam failure recovery procedure, including the transceiver transmitting the beam failure recovery signal using the dedicated uplink radio resources from the allocation; wherein the dedicated uplink radio resources are restricting the transmission to a subset of the plurality of uplink beams that can be exclusively allocated by the base station to the mobile terminal.

BACKGROUND Technical Field

The present disclosure relates to an uplink resource allocation for amobile terminal to transmit a beam failure recovery signal in responseto it having detected a downlink beam failure event when communicatingin a mobile communication system with a base station.

Description of the Related Art

Currently, the 3^(rd) Generation Partnership Project (3GPP) focuses onthe next release (Release 15) of technical specifications for the nextgeneration cellular technology, which is also called fifth generation(5G).

At the 3GPP Technical Specification Group (TSG) Radio Access network(RAN) meeting #71 (Gothenburg, March 2016), the first 5G study item,“Study on New Radio Access Technology” involving RAN1, RAN2, RAN3 andRAN4 was approved and is expected to become the Release 15 work item(WI) which will define the first 5G standard.

One objective of 5G new radio (NR) is to provide a single technicalframework addressing all usage scenarios, requirements and deploymentscenarios defined in 3GPP TSG RAN TR 38.913 v14.1.0, “Study on Scenariosand Requirements for Next Generation Access Technologies”, December 2016(available at www.3gpp.org and incorporated herein in its entirety byreference), at least including enhanced mobile broadband (eMBB),ultra-reliable low-latency communications (URLLC), massive machine typecommunication (mMTC).

For example, eMBB deployment scenarios may include indoor hotspot, denseurban, rural, urban macro and high speed; URLLC deployment scenarios mayinclude industrial control systems, mobile health care (remotemonitoring, diagnosis and treatment), real time control of vehicles,wide area monitoring and control systems for smart grids; mMTC mayinclude the scenarios with large number of devices with non-timecritical data transfers such as smart wearables and sensor networks.

Another objective is the forward compatibility, anticipating future usecases/deployment scenarios. The backward compatibility to Long TermEvolution (LTE) is not required, which facilitates a completely newsystem design and/or the introduction of novel features.

As summarized in one of the technical reports for the NR study item(3GPP TSG TR 38.801 v2.0.0, “Study on New Radio Access Technology; RadioAccess Architecture and Interfaces”, March 2017), the fundamentalphysical layer signal waveform will be based on Orthogonal FrequencyDivision Multiplexing (OFDM). For both downlink and uplink, OFDM withcyclic prefix (CP-OFDM) based waveform is supported. Discrete FourierTransformation (DFT) spread OFDM (DFT-S-OFDM) based waveform is alsosupported, complementary to CP-OFDM waveform at least for eMBB uplinkfor up to 40 GHz.

As summarized in another of the technical reports for the NR study item(3GPP TSG TR 38.802 V2.0.0, “Study on New Radio (NR) Access Technology;Physical Layer Aspects” a multi-antenna scheme relies on a set of beammanagement procedures. This procedures enable the transmit receivepoints (TRPs) and/or the UE to acquire and maintain a set of beams thatcan be used for DL and UL transmission/reception, including beamdetermination, beam measurement, beam reporting and beam sweeping.

One of the design targets in NR is to utilize the fundamental physicallayer signal waveform in communications while increasing the coveragewith base stations supporting single-user and multi-user MIMO in bothdownlink and uplink. For this purpose, it was agreed in the 3GPP TSGRAN1 WG1 Meeting #89, Hangzhou, P.R. China 15-19 May 2017 to employ beammanagement procedures including a beam failure recovery mechanism incase a beam failure is detect. This mechanism is separate from radiolink failure procedures in upper layers.

The term “downlink” refers to communication from a higher node to alower node (e.g., from a base station to a relay node or to a UE, from arelay node to a UE, or the like). The term “uplink” refers tocommunication from a lower node to the higher node (e.g., from a UE to arelay node or to a base station, from a relay node to a base station, orthe like). The term “sidelink” refers to communication between nodes atthe same level (e.g., between two UEs, or between two relay nodes, orbetween two base stations).

BRIEF SUMMARY

One non-limiting and exemplary embodiment facilitates the beam failurerecovery procedure to be initiated in a robust (reliable) manner, namelyby utilizing dedicated uplink radio resources on a more efficient(situation-dependent) basis.

In one general aspect, the techniques disclosed here feature, a mobileterminal for communicating in a mobile communication system with a basestation using at least one of a plurality of downlink beams and at leastone of a plurality of uplink beams, each of the downlink and uplinkbeams having different directivities and/or coverage, comprising: which,in operation, receives for a beam failure recovery, BFR, procedure anallocation of dedicated uplink radio resources for transmitting a beamfailure recovery signal, a processor which, in operation, detects adownlink beam failure event and, in response thereto, initiates the beamfailure recovery procedure, including the transceiver transmitting thebeam failure recovery signal using the dedicated uplink radio resourcesfrom the allocation; wherein the dedicated uplink radio resources arerestricting the transmission to a subset of the plurality of uplinkbeams that can be exclusively allocated by the base station to themobile terminal.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of a mobile terminal anda base station;

FIG. 2 is schematic drawings illustrating a beam failure recoveryprocedure initiation in the context of a 4-step beam failure recoveryprocedure in a general deployment scenario;

FIG. 3 is schematic drawings illustrating a beam failure recoveryprocedure initiation in the context of a 4-step beam failure recoveryprocedure in a 3GPP NR deployment scenario;

FIG. 4 is schematic drawings illustrating a beam failure recoveryprocedure initiation in the context of a 2-step beam failure recoveryprocedure in a 3GPP NR deployment scenario;

FIG. 5 is schematically illustrating dedicated uplink radio resources ina physical random access channel, PRACH for initiation of the beamfailure recovery procedure;

FIG. 6 is schematically illustrating dedicated uplink radio resources ina physical uplink control channel, PUCCH for initiation of the beamfailure recovery procedure; and

FIGS. 7a-7b are schematic drawings illustrating main causes of adownlink beam failure in a 3GPP NR deployment scenario.

DETAILED DESCRIPTION

In another general aspect, the techniques disclosed here feature,another mobile terminal for communicating in a mobile communicationsystem with a base station using at least one of a plurality of downlinkbeams and at least one of a plurality of uplink beams, each of thedownlink and uplink beams having different directivities, comprising:which, in operation, receives for a beam failure recovery, BFR,procedure an allocation of dedicated uplink radio resources fortransmitting a beam failure recovery signal, a processor which, inoperation, detects a downlink beam failure event and, in responsethereto, initiates the beam failure recovery procedure, including thetransceiver transmitting the beam failure recovery signal using thededicated uplink radio resources of the previous allocation; wherein thededicated uplink radio resources are restricting the transmission to asubset of the plurality of uplink beams that can be non-exclusivelyallocated by the base station to the mobile terminal.

In further general aspect, the techniques disclosed here feature, amethod for initiating a beam failure recovery procedure to be performedby a mobile terminal configured to communicate in a mobile communicationsystem with a base station using at least one of a plurality of downlinkbeams and at least one of a plurality of uplink beams, each of thedownlink and uplink beams having different directivities and/orcoverage, the method comprising the steps of: receiving for a beamfailure recovery, BFR, procedure an allocation of dedicated uplink radioresources for transmitting a beam failure recovery signal, detecting adownlink beam failure event and, in response thereto, initiating thebeam failure recovery procedure, including transmitting the beam failurerecovery signal using the dedicated uplink radio resources from theallocation; wherein the dedicated uplink radio resources are restrictingthe transmission to a subset of the plurality of uplink beams that canbe exclusively allocated by the base station to the mobile terminal.

In yet another general aspect, the techniques disclosed here feature,another method for initiating a beam failure recovery procedure to beperformed by a mobile terminal configured to communicate with a basestation using at least one of a plurality of downlink beams and at leastone of a plurality of uplink beams, each of the uplink and downlinkbeams having different directivities, comprising: receiving for a beamfailure recovery, BFR, procedure an allocation of dedicated uplink radioresources for a beam failure recovery signal, detecting a downlink beamfailure event and, in response thereto, initiating the beam failurerecovery procedure, including transmitting the beam failure recoverysignal using the dedicated uplink radio resources of the previousallocation; wherein the dedicated uplink radio resources are restrictingthe transmission to a subset of the plurality of uplink beams that canbe non-exclusively allocated by the base station to the mobile terminal.

As identified in TR 38.913, the various use cases/deployment scenariosfor NR have diverse requirements in terms of data rates, latency, andcoverage. With these requirements in mind NR should aim for even highercoverage, as compared with LTE.

In 3GPP RAN1 #85, beam based transmissions have been discussedextensively for NR as a key technology to ensure coverage. It was agreedfor beam management that both intra-TRP and inter-TRP beamformingprocedures are considered, and beamforming procedures are consideredwith/without TRP beamforming/beam sweeping and with/without UEbeamforming/beam sweeping, according to the following potential usecases: UE movement, UE rotation, beam blocking (change of beam at TRP,same beam at UE; same beam at TRP, change of beam at UE; or change ofbeam at TRP, change of beam at UE) where other cases are not precluded.It was further agreed to study beam (e.g., TRP beam(s) and/or UEbeam(s)) management procedure (e.g., beam determination and changeprocedure) with/without prior acquired beam(s) information, namely forboth data and control transmission/receptions, where the procedures mayor may not be the same for data and control.

Subsequently, in RAN1 #88, the following agreements were reached: Beamfailure event occurs when the quality of beam pair link(s) of anassociated control channel falls low enough (e.g., comparison with athreshold, time-out of an associated timer). Mechanism to recover frombeam failure is triggered when beam failure occurs. Note: the beam pairlink is used for convenience, and may or may not be used inspecification. It remained for further study, FFS: whether quality canadditionally include quality of beam pair link(s) associated withNR-PDSCH; when multiple Y beam pair links are configured, X (<=Y) out ofY beam pair links falls below certain threshold fulfilling beam failurecondition may declare beam failure; search space (UE-specific vs.common) of the associated NR-PDCCH; what the signaling mechanisms forNR-PDCCH are in the case of UE is configured to monitor multiple beampair links for NR-PDCCH. Further, the exact definition of such thresholdis FFS and other conditions for triggering such mechanism are notprecluded.

It was also agreed that the following signals can be configured fordetecting beam failure by UE and for identifying new potential beams byUE, yet remaining FFS the reference to the signals, e.g., RS for beammanagement, RS for fine timing/frequency tracking, SS blocks, DM-RS ofPDCCH (including group common PDCCH and/or UE specific PDCCH), DM-RS ofPDSCH. If beam failure event occurs and no new potential beams weredetected by the UE in the serving cell, it has remained for FFS whetheror not the UE provides an indication to L3, and whether or not theindication links to the radio link failure event. Note: the criterionfor declaring radio link failure is for RAN2 to decide. Also for FFS isthe necessity of such indication. NR supports configuring resources forsending request for recovery purposes in symbols containing RACH and/orFFS scheduling request or in other indicated symbols.

Then, in RAN1 #88Bis it was agreed that UE beam failure recoverymechanism includes the following aspects: beam failure detection; newcandidate beam identification; beam failure recovery requesttransmission; where the UE monitors gNB response for beam failurerecovery request. In beam failure detection, UE monitors beam failuredetection RS to assess if a beam failure trigger condition has been met;where beam failure detection RS at least includes periodic CSI-RS forbeam management; and where sounding signal, SS-block within the servingcell can be considered, if SS-block is also used in beam management aswell. It has however been left FFS what Trigger condition are fordeclaring beam failure.

Regarding the new candidate beam identification it was also agreed thatUE monitors beam identification RS to find a new candidate beam; and thebeam identification RS includes Periodic CSI-RS for beam management, ifit is configured by NW; and/or periodic CSI-RS and SS-blocks within theserving cell, if SS-block is also used in beam management as well

Regarding the beam failure recovery request transmission was also agreedthat the information carried by beam failure recovery request includesat least one followings: explicit/implicit information about identifyingUE and new gNB TX beam information; explicit/implicit information aboutidentifying UE and whether or not new candidate beam exists. Thefollowing was left FFS: information indicating UE beam failure;additional information, e.g., new beam quality. A down-selection betweenthe following channels for beam failure recovery request transmissionwas agreed to include PRACH; PUCCH; PRACH-like (e.g., differentparameter for preamble sequence from PRACH). Beam failure recoveryrequest resource/signal may be additionally used for scheduling request.

In this regard, the UE monitors a control channel search space toreceive gNB response for beam failure recovery request, where it is FFS:if the control channel search space can be same or different from thecurrent control channel search space associated with serving BPLs,and/or what the UEs further reaction are if gNB does not receive beamfailure recovery request transmission.

Thus, it may be concluded that beam failure recovery procedure discussedabove facilitates an efficient way to re-establish a connection betweenthe UE and the gNB (i.e., TRP) after a downlink beam failure event,namely without the necessity of declaring a radio link failure to higherlayers. Nevertheless it was recognized that this beam failure recoveryprocedure can only be successful if it provides measures which allow theUE to act quickly before the radio link failure event has beentriggered.

In other words, the concept of recovering after a beam failure builds onthe procedure that the UE, after detecting a beam failure for thedownlink beam, indicates to the gNB an alternative (i.e., candidate)downlink beam over which the communication between the gNB and the UEcan be recovered. Hence, the procedure relies on the UE being stillcapable of indicating to the gNB alternative (i.e., candidate) downlinkbeams. This, however, is only possible for a short period of time afterthe downlink beam failure has occurred.

Consequently, one non-limiting exemplary embodiment of the presentdisclosure suggests a robust mechanism that will enable the UE torespond to the beam failure detection event by initiating the beamfailure recovery procedure as quickly as possible in order to avoid anydeteriorating-effects which are resulting from the inherentcorrespondence between downlink beam and the uplink beam.

The suggested robust mechanism can even better be understood whenturning to the origin or cause for the beam failures in thecommunication between the gNB and the UE. This understanding isgenerally based on, however not restricted to, a deployment scenario of3GPP NR, namely where the concept of beams is introduced to improvedirectivity and/or coverage. This is particularly advantageous in viewof the envisioned very high frequency bands (millimeter wave) in which3GPP NR is intended to operate.

As shown in FIGS. 7a and 7b , a gNB can be configured to communicate onmultiple beams (e.g., beam #0 to beam #4). This is necessary for theinitial access by the UE. After having established a connection betweenthe gNB and the UE, the gNB serves the UE with a downlink on a singlebeam (termed “downlink serving beam” or “downlink beam”). Having saidthis, it shall be appreciated that multiple-beam scenarios can also beenvisioned, namely where the gNB serves the UE with a downlink via twoor more separate beams, for instance to increase capacity.

Similarly, the UE can be configured to communicate on multiple beams(e.g., beam #0 to beam #4). This is equally necessary for the initialaccess by the UE. After having established the connection, the UE issending uplink traffic to the gNB with an uplink also on a single beam(termed “uplink serving beam” or “uplink beam”). This single uplinkserving beam is, however, not necessarily the same as the beam on whichthe downlink is served. Also in the uplink, multiple-beam scenarios canbe envisioned such that the disclosure shall not be construed as beinglimited in any respect.

In general, it can be assumed that the pair(s) of downlink and uplinkserving beams has suitable properties for the downlink and uplinkcommunication between the gNB and the UE. In many cases, it can bereadily understood that there is a correspondence in directivity betweenthe pair(s) of downlink serving beam and uplink serving beam, namelythat the pair of downlink and uplink serving beams are beams havingopposite directions and similar coverage.

In this context it shall be mentioned that a gNB in 3GPP NR isconfigured with one or multiple TRP (Transmit/Receive Points or Tx/RxPoints), each TRP being linked to a downlink and/or uplink serving beamwith a specific direction and a specific coverage. Thus, for amulti-beam configuration, the gNB would necessarily be configured withmore than one TRP, namely to be capable of transmitting/receiving beamswith different directions and/or coverage.

Coming back to the origin or cause for the beam failure, it can beimmediately derived from the figures that one main cause of beamfailures (cf. FIG. 7a ) is an obstacle which inhibits a propagation ofthe serving beam(s) between the gNB and the UE and vice-versa. Anothermain cause of beam failures (cf. FIG. 7b ) is a movement of the UE withrespect to the gNB, thereby resulting in the beams propagating ininappropriate directions.

With this understanding, it can however be appreciated that both maincauses do not necessarily affect the pair(s) of downlink and uplinkserving beams in a same fashion. In other words, should the downlinkcommunication be served on a beam with a direction other than that ofthe beam serving the uplink communication, it may very well be that onlyone of the downlink and uplink beams is undergoing beam failure.

There may even be cases where, in case of a closer distance between theobstacle and the UE as opposed to the obstacle and the gNB, the uplinkserving beam does not undergo beam failure at the close distance, butthe downlink serving beam does undergo beam failure at the fartherdistance.

Hence, it has been readily recognized that there is a need for beamfailure recovery procedure, namely in situations when the downlinkserving beam undergoes beam failure but the uplink serving beam is stilloperational. In this situation, a beam failure recovery request may besent by the UE indicating alternative (i.e., candidate) downlink beamsfor serving the downlink communication.

The present disclosure provides a robust mechanism that enables the UEto respond to the detection of a downlink beam failure event whilereducing the amount of uplink radio resources that are blocked(assigned) for initiating the beam failure recovery procedure. Thismechanism is particularly suitable for a proposed scenario in 3GPP NRaccording to which the beam failure recovery procedure relies oncontention-free physical random access channel, PRACH, resources orcontention-free physical uplink control channel, PUCCH, resources.

As apparent from this scenario, using a contention-free PRACH or PUCCHresource for the beam failure recovery procedure has advantages as wellas drawbacks. Relying on contention-free resources on an uplink beamfacilitates an immediate access by the UE to signal to the gNB that thebeam failure event has been detected for a downlink beam. However, dueto the uncertainty when in time and under what directivity conditionsthe radio link failure is detected, the UE would have to be allocatedwith all potentially available combinations for it to successfullyinitiate the beam failure recovery procedure.

This uncertainty would result in each UE blocking a vast amount ofdedicated uplink radio resources, particular in the case of thesuggested contention-free physical random access channel, PRACH,resources or contention-free physical uplink control channel, PUCCH,resources. In view of the envisioned large number of UEs that are to beserved by each gNB, this results in a large overhead of dedicated uplinkradio resources which cannot be used for other purposes. Consequently,the approach clearly conflicts with existing design principles accordingto which resources (particularly scarce resources) shall be onlyallocated by the gNB (thus blocked) if they are required and expected tobe used in the near future by the UE.

The present disclosure provides solutions to mitigate these drawbackswhile still allowing the beam failure recovery procedure to be initiatedin a robust (reliable) manner, namely by utilizing dedicated uplinkradio resources on a more efficient (situation-dependent) basis.

Generally, the present disclosure provides devices and methods for autilization of dedicated uplink radio resources to initiate a beamfailure recovery procedure not for all potentially available but onlyfor the relevant constellations that are (actually) expected to beencountered should the beam failure event be detected. As the relevantconstellations may change over time, the dedicated uplink radioresources can be flexibly (re-)allocated without incurring a largesignaling overhead.

For this purpose, it is proposed that the gNB allocates to an UE uplinkradio resources, dedicated for the initiation of the beam failurerecover procedure, on a restricted but efficient basis, namely byrestricting a signaling of a beam failure recovery signal to only asubset of all potentially available uplink beam that can be exclusivelyor non-exclusively allocated by the gNB to the UE. Having restricteddedicated uplink radio resources to a subset, for example one, two orthree uplink beams out of the maximum number of, say ten, potentiallyavailable uplink beams, the blockage of same dedicated uplink radioresources is far less compromising to the operation of the wirelesscommunication system.

Notably, this effectively contrasts the alternative approach of a beamfailure recovery procedure where the beam failure recovery signal istransmitted in a full beam sweeping manner (i.e., successively utilizingall potentially available uplink beams for the transmission of beamfailure recovery signal). For this beam sweeping it would be required toallocate (hence block) dedicated uplink radio resources on allpotentially available uplink beams.

Incremental thereto, it is proposed to employ an efficient mechanism for(re-) allocating same dedicated uplink radio resources which can ensurethat the gNB allocates to the UE only the most pertinent dedicateduplink radio resources. For each (actual) situation the UE must still becapable of initiating, upon detection of a downlink beam failure event,a beam failure recovery procedure. In this context, it may beadvantageous to reduce blockage if the (re-) allocation of the dedicateduplink radio resources expires after a given time period, or if the(re-)allocation of the dedicated uplink radio resources is updated on aperiodic basis.

FIG. 1 illustrates a block diagram of the wireless communication systemincluding a mobile terminal 110 and a base station 160 communicatingwith each other using at least one of a plurality of downlink beams andat least one of a plurality of uplink beams. In other words, thecommunication between the mobile terminal 110 and the base station 160is taking place on a pair of a downlink and an uplink (serving) beam150.

In the context of the present disclosure, the term beam is to beconstrued as having a specific (pre-determined) directivity and/orcoverage. Each of the uplink beams as well as each of the downlink beamshas a different directivity and/or coverage, thereby resulting inability for the transmitter to transmit signal to a receiver atdifferent (spatial) positions. In other words, each of the uplink beamsas well as each of the downlink beams has different spatial parameters(e.g., gain and/or beam width)

The mobile terminal 110 comprises a transceiver 120 which, in operation,receives from the base station 160 for a beam failure recovery, BFR,procedure an allocation of dedicated uplink radio resources for sendinga beam failure recovery signal. Further, the mobile terminal 110comprises a processor 130 which, in operation, detects a downlink beamfailure event and, in response thereto, initiates the beam failurerecovery procedure, including the transceiver 120 transmitting to thebase station 160 the beam failure recovery signal using the dedicateduplink radio resources from the allocation.

Notably, the dedicated uplink radio resources, allocated to the mobileterminal 110, are restricting the transmission to a subset of theplurality of uplink beams that can be exclusively allocated by the basestation 160. Thereby, not all but only the subset of dedicated uplinkradio resources is blocked from being used in an exclusive manner byanother mobile terminal.

Alternatively, the dedicated uplink radio resources, allocated to themobile terminal 110, are restricting the transmission to a subset of theplurality of uplink beams that can be non-exclusively allocated by thebase station 160. Thereby, also here not all but only the subset ofdedicated uplink radio resources is blocked from being used in anon-exclusive manner by another mobile terminal.

In the context of the present disclosure a distinction is made betweenan exclusive and a non-exclusive allocation of dedicated uplink radioresources on uplink beams. An exclusive allocation shall be construed ina sense such that no other mobile terminal is allocated, for a same timeperiod, with a same dedicated uplink radio resource, including a sameuplink beam. In contrast, a non-exclusive allocation shall be construedin the sense such that possibly other mobile terminals are allocated,for a same time period, with the same dedicated uplink radio resource,including a same uplink beam.

The base station 160 comprises a transceiver 170 which, in operation,transmits to the mobile terminal 110 for a beam failure recovery, BFR,procedure an allocation of dedicated uplink radio resources for themobile terminal 110 to send a beam failure recovery signal. Further, thebase station 160 comprises a processor 180 which, in operation, performsthe beam failure recovery procedure in response to the transceiver 170receiving from the mobile terminal 110 the beam failure recovery signalusing the dedicated uplink radio resources from the allocation.

Notably, also here the dedicated uplink radio resources, allocated bythe base station 160, are restricting the transmission to a subset ofthe plurality of uplink beams that can be exclusively allocated to themobile terminal 110. Thereby, not all but only the subset of dedicateduplink radio resources is blocked from being used in an exclusive mannerby another mobile terminal.

Alternatively, the dedicated uplink radio resources, allocated by thebase station 160, are restricting the transmission to a subset of theplurality of uplink beams that can be non-exclusively allocated to themobile terminal 110. Thereby, also here not all but only the subset ofdedicated uplink radio resources is blocked from being used in anon-exclusive manner by another mobile terminal.

The initiation of the beam failure recovery procedure and moreparticularly the allocation of dedicated uplink radio resources shall beexplained in further detail with respect to FIG. 2. In particular, thisfigure puts the present disclosure into the context of an exemplary4-step beam failure recovery procedure. Notably, the present disclosureshall not be construed as being limited in any respect.

In FIG. 2, the mobile terminal 110 (also termed UE) and the base station160 (also termed gNB) are communicating in a wireless communicationnetwork using a pair of a downlink and an uplink (serving) beams 150. Inparticular, the pair of the downlink and uplink beams is one of aplurality of downlink beams and one of a plurality of uplink beams thatcan be configured by the base station 160 in the mobile terminal 110.

For the beam failure recovery procedure, the mobile terminal 110 isallocated (S01—FIG. 2) by the base station 160 with dedicated uplinkradio resources. As mentioned earlier, the allocation of these uplinkradio resources is dedicated for use with beam failure recoverysignaling. In other words, this dedication of the uplink radio resourcescan prevent it from being used in a different context. In any case, thededication of the uplink radio resource enables the base station 160 toidentify (recognize) and initiate the associated functionality (i.e.,initiate the beam failure recovery procedure) when receiving the beamfailure recovery signaling on the dedicated uplink radio resource.

In addition, the allocation of the dedicated uplink radio resources mayinclude an instruction from the base station 160 that for the purposesof the beam failure recovery procedure, the mobile terminal 110 shallinclude its identification (e.g., a radio network terminal identifier,RNTI) in subsequent messages of the beam failure recovery procedure.This can be particularly advantageous, in case the mobile terminal 110is not-exclusively but instead non-exclusively allocated the dedicateduplink radio resources, which is however discussed further below.

Subsequently, the mobile terminal 110 detects a downlink (also termedDL) beam failure event, i.e., a beam failure for the downlink (serving)beam of the beam pair 150 over which the base station 160 and the mobileterminal 110 are communicating with each other. Two main causes for beamfailures, namely an obstacle and an UE movement, have already beendiscussed above.

Further, there are numerous ways for the mobile terminal 110 to detectthe beam failure event for the downlink (serving) beam, for instance bymeasuring the reference signal received power, RSRP, or the referencesignal received quality, RSRQ, on this (serving) downlink beam anddetermining that the measurement has fallen below a given threshold.Other ways for the mobile terminal 110 to detect the beam failure eventfor the downlink (serving) beam may include a lapse of given (countdown)timer, namely when the periodic control and/or user data has not beenreceived within the time period defined by the given (countdown) timer.

In this respect, the beam failure event may be understood as an eventwhich may directly (i.e., by measurements) or indirectly (i.e., by lapseof a timer) be detected in the mobile terminal 110.

In response to the detection of the downlink beam failure event, themobile terminal 110 transmits (S02—FIG. 2) the beam failure recoverysignal to the base station 160. Notably, the beam failure recoverysignal is using the dedicated uplink radio resources which wereallocated beforehand. As already mentioned before, due to the fact thatdedicated uplink radio resources are used, the base station 160 canimmediately identify (recognize) and initiate the associatedfunctionality (i.e., initiate the beam failure recovery procedure).

In case the number of uplink beams is larger than one that form thesubset on which the failure recovery signal is transmitted, then themobile terminal 110 may also transmit this signal in a beam sweepingmanner. This is however, due to the restriction to a subset of allpossibly available uplink beams, more efficient than a beam failurerecovery signal which is transmitted in a full (not only part) beamsweeping manner.

Most importantly, the allocation of the dedicated uplink radio resourcesis restricting the transmission to a subset of the plurality ofpotentially available uplink beams. This restriction to the subset ofuplink beams is enforced irrespective of whether the dedicated uplinkradio resources are exclusively allocated or non-exclusively allocatedby the base station 160 to the mobile terminal 110. The dedicated uplinkradio resources may be restricted to the subset, for example to one, twoor three uplink beams out of the maximum number of, say ten, potentiallyavailable uplink beams.

Having received the beam failure recovery signal, this however does not(yet) put the base station 160 in a position that it can complete thebeam failure recovery procedure for the downlink beam for which themobile terminal 110 has detected the beam failure. As discussed before,the beam failure recovery procedure also includes transmitting a messagewhich allows explicitly or implicitly indicating by the mobile terminal110 to the base station 160 alternative (candidate) downlink beams withwhich the beam failure can be recovered.

For this purpose, the base station 160 transmits (S03—FIG. 2) a beamfailure recovery control signal to the mobile terminal 110. Most likelythis control signal includes an uplink grant such that the mobileterminal 110 can effect the transmission of the alternative (candidate)downlink beams. This control signal is however not restricted to theuplink grant only.

In addition, this control signal may also include an instruction fromthe base station 160 that for the purposes of the beam failure recoveryprocedure, the mobile terminal 110 shall include its identification(e.g., a radio network terminal identifier, RNTI) in subsequent messagesof the beam failure recovery procedure. This can be particularlyadvantageous, in case the mobile terminal 110 is not exclusively butinstead non-exclusively allocated the dedicated uplink radio resources,which is however discussed further below.

With reference to the received uplink grant, the mobile terminal 110transmits (S04—FIG. 2) a beam failure recovery request to the basestation 160. This request includes at least one of the following: anexplicit or implicit information about identifying the mobile terminal110 and new downlink beam candidate information for the base station160; an explicit or implicit information about identifying the mobileterminal 110 and whether or not new downlink beam candidates exist.

With this information, the base station 170 is capable of recoveringfrom beam failure on the downlink beam, namely by for instance revertingto one of the explicitly or implicitly indicated new downlink beamcandidate information. This information about new downlink candidatebeams can, exemplarily, be obtained from downlink reference signals thatare continuously transmitted by the base station 160 on all potentiallyavailable downlink beams. By measuring these downlink reference signals,the mobile terminal 110 can identify new downlink beam candidates.

In response to the beam failure recovery request, the base station 160transmits (S05—FIG. 2) a beam failure recovery response to the mobileterminal 110. This response is a response to the beam failure recoveryrequest transmitted by the mobile terminal 110 before. In particular,only after this response is received by the mobile terminal 110, itknows that the information indicating new downlink beam candidates hasbeen successfully received, and has been put into practice.

Notably, a successful beam failure recovery is also possible when thebeam failure recovery request, transmitted by the mobile terminal 110 tothe base station 160170 does not include any new downlink beam candidateinformation for the base station 160 (instead the request includes theinformation that no new downlink beam candidates exist), In this case,the new downlink (serving) beam is then determined by the base station160 iself170.

In particular, when the mobile terminal 110 has not suggested any newdownlink beam candidate, the base station 160 may instead determine towhich downlink beam it is to recover its communication with the mobileterminal 110. For this, the base station may refer to reports on themeasurements of downlink reference signals (in 3GPP NR terminology e.g.,CSI-RS) it has (previously) obtained from the mobile terminal 110.

Having determined a new downlink beam, the base station 160 still has toinform the mobile station 110 on the new downlink beam. Only then canboth the base station 160 and the mobile terminal 110 revert to the samenew pair of the new downlink and the current uplink (serving) beams.Accordingly, after determination of a new downlink beam, the basestation 160 includes information on this new downlink beam also in thebeam failure recovery response to the mobile terminal 110.

For example, the beam failure recovery response from the base station160 may mark the point in time when the mobile terminal 110 switches thecommunication over to new beam pair including the new downlink beam asnew downlink (serving) beam. In a further example, the absence of thebeam failure response from the base station 160 within a given timeperiod may result in the mobile terminal 110 determining that the beamfailure recovery procedure has not been successful, thus, signaling aradio link failure event to upper layers.

In summary, a description of a 4-step beam failure recovery procedure isgiven in connection with the FIG. 2, namely where the steps S02, S03,S04 and S05 of the figure resemble the individual 4-steps of theprocedure. In other words, the step S01 of the figure is moreoverpreparatory nature and, for this purpose is not considered part of the4-step beam failure recovery procedure.

Independent of this complete presentation of the beam failure recoveryprocedure, it shall again be emphasized that the present disclosure isfocused on proposing a robust and efficient mechanism for initiating(not concluding) the beam failure recovery procedure. Due to this narrowfocus, the steps S03, S04 and S05 of the figure must be consideredoptional for attaining this effect. The initiation of the beam failurerecovery procedure does not become more robust or efficient, if theprocedure completes successful or not, there is simply no connection tothe focus which is laid out herein.

Exclusive and Non-exclusive Allocation

As mentioned before, the base station 160 can allocate dedicated uplinkradio resources to the mobile terminal 110 in an exclusive or anon-exclusive manner. Even though this appears to be a small detail, ithas a major impact on the beam failure recovery procedure as shallbecome apparent from the following.

Considering an exclusive allocation, the base station 160, after receiptof the beam failure recovery signal in S02—FIG. 2, knows exactly towhich mobile terminal it has to address the control signal in S03—FIG.2. Due to the fact that the dedicated uplink radio resources areexclusively allocated to only one mobile terminal 110, the base station160 can derive from the dedicated uplink radio resources the mobileterminal 110 which has been using same. Consequently, the base station160 can address the subsequent control signal 110 also to this mobileterminal 110.

Considering a non-exclusive allocation, the base station 160, afterreceipt of the beam failure recovery signal in S02—FIG. 2 does not know(as such) to which mobile terminal it has to address the control signalin S03—FIG. 2. For this purpose, it is suggested that base station 160examines the context under which the beam failure recovery signal isreceived, and tries to infer which mobile terminal it has received thesignal from. As becomes immediately apparent, if the dedicated uplinkradio resources were allocated albeit non-exclusively to only a smallnumber of, say two, mobile terminals, then the context gives more easilyaway from which mobile terminal the signal was received.

One possibility ties in with the fact that only a subset of theplurality of all potentially available number of uplink beams isallocated to a base station as dedicated uplink radio resources for thebeam failure recovery signal. For example, if say one uplink beams isallocated as the subset to each of, say two mobile terminals in anon-exclusive manner, then this subset reduces the number of mobileterminals from which the signal can originate.

Nevertheless, for this possibility, the base station still has topredict based on the context, for example, based on most recent beamstatus updates, which mobile terminal from among the reduced number ofmobile terminals, has used the non-exclusively allocated dedicateduplink radio resources, and has thereon (actually) transmitted the beamfailure recovery signal. Already here, it shall be appreciated that thesubset again enables the base station to better identify the mobileterminal from which the signal originates.

Given the case that the base station cannot or fails to predict (with areasonable degree of certainty) from which mobile terminal the signaloriginates, it can decide to transmit the beam failure recovery controlsignal of S02—FIG. 2 to more than one, in the above example to the two,mobile terminals which have both been non-exclusively allocated the samededicated uplink radio resources.

In this case, it is advantageous as discussed before, if the mobileterminal is instructed to include its identification in the subsequentmessages, namely in the beam failure recovery request, i.e., of S04—FIG.2. From this included identification information in the beam failurerecovery request, the base station can conclude on the correct mobileterminal for which the beam failure recovery procedure shall be carriedout. For the other incorrectly predicted mobile terminal it will stopthe beam failure recover procedure.

Another possibility ties in with the fact that the beam failure recoverysignal may be transmitted on a dedicated uplink radio resource whichitself requires additional control information to be appended. Thisappended control information may be used by the base station to identifythe mobile terminal as the origin of the signal.

This is for example the case where the beam failure recovery signal istransmitted via a physical uplink control channel, PUCCH. The 3GPP NRspecification of the PUCCH prescribes the mobile terminal not only totransmit uplink control information, UCI, of a given format, but also toappend thereto transmission demodulation reference signals, DM-RS, whichare uniquely assigned to each mobile terminal.

Thus, having received a beam failure recovery signal in an UCI on thePUCCH, the base station can identify from the DM-RS the mobile terminalthat has transmitted this signal. Also here the context is decisive forthe base station to identify the mobile terminal in order to address thesubsequent beam failure recovery control signal in S03—FIG. 2 to thecorrect mobile terminal.

FIG. 3 now assumes a 3GPP NR deployment scenario. In more detail, thisfigure depicts the initiation of beam failure recovery procedure in thecontext of a 4-step beam failure recovery procedure, where the UE andthe gNB communicate over a pair of downlink and uplink beams. Also herea pair of downlink and uplink (serving) beams are one of a plurality ofdownlink beams and one of a pair of uplink beams that can be configuredby the gNB in the UE.

For the beam failure recovery procedure, the UE is allocated (S11—FIG.3) by the gNB with dedicated uplink radio resources. As mentionedearlier, the allocation of uplink radio resources is dedicated for theuse with beam failure recovery signaling. For this purpose, the gNBtransmits a radio resource configuration, RRC; connectionreconfiguration message to the UE. Alternatively, also an RRC connectionsetup message may be used for allocation purposes.

In another example, the UE is allocated with dedicated uplink radioresources via a downlink medium access control, MAC, control element,CE, a downlink control information, DCI, and a control protocol dataunit, PDU of a packet data convergence protocol, PDCP. In particular,the PDCP control PDU has even the advantage that the signaling overheadis slightly less when compared to a RRC connection reconfigurationmessage. Thus, this can result in a further increase in signaling speed.

Separate from an allocation through a single message, the allocation canalso be achieved by a first message configuring the dedicated uplinkradio resources, and a second, subsequent message activating theconfiguration. In this case, the UE receives from the gNB aconfiguration of the dedicated uplink radio resources via an RRCconnection setup or reconfiguration message, and (subsequently) anactivation of the dedicated uplink radio resources from theconfiguration via one of MAC CE, a DCI, and a PDCP control PDU.

This message may include a reference to a dedicated uplink radioresource of a physical random access channel, PRACH, namely one of acontention-free resource, preferably a contention-free preamble sequencewith a time and frequency reference on an uplink beam.

Reference is made to contention-free preamble sequences only. This isdue to the fact that in 3GPP NR the gNB only (actively) assigns thesetypes of preamble sequence to an UE. In contrast, for non-contentionfree (contention-based) preamble sequences, the gNB cannot distinguishwhether these sequences are being used by an UE for initiation of thebeam failure recovery procedure, or whether a (conventional)time-alignment procedure is being carried out. This rules out any usageof the non-contention free (contention-based) preamble sequences asdedicated uplink radio resources for the initiation of the beam failurerecovery procedure.

Assuming, for example, the configuration shown in FIG. 5, the messagemay include a reference to a PRACH with a preamble sequence index S1, atime reference T1, and a frequency reference F1 on uplink beam #1.Thereby, the UE is allocated with a dedicated uplink radio resource withwhich it can initiate the beam failure recovery procedure. In thisexample, the time reference T1 may be understood as an offset indicatinga slot which is offset in time from each radio frame boundary.Additionally, the frequency reference F1 may be understood as an indexof a resource block.

Alternatively this message may also include a reference to a dedicateduplink radio resource of a physical uplink control channel, PUCCH,namely to a contention-free uplink control information, UCI, of a givenformat with a time and frequency reference on an uplink beam. Assuming,for example, the configuration shown in FIG. 6, the message may includea reference to a PUCCH with a time reference T1 and a frequencyreference F1 on beam #1.

In both examples, namely the contention-free PRACH or PUCCH, thededication of the uplink radio resources can prevent it from being usedin a different context. In any case, the dedication of the uplink radioresource enables the gNB to identify (recognize) and initiate theassociated functionality (i.e., initiate the beam failure recoveryprocedure) when receiving the beam failure recovery signaling on thededicated uplink radio resource.

In response to the detection of the beam failure event, the UE transmits(S12—FIG. 3) the beam failure recovery signal to the gNB. Notably, thebeam failure recovery signal is using the dedicated uplink radioresources namely the contention-free PRACH or PUCCH, which wereallocated beforehand. As already mentioned before, due to the fact thatdedicated uplink radio resources are used, the gNB can immediatelyidentify (recognize) and initiate the associated functionality (i.e.,initiate the beam failure recovery procedure). Notably, the PRACHresource implicitly indicates a scheduling request, SR, whereas the UCIof the given format may explicitly or implicitly include the SR.

Having received the dedicate PRACH or PUCCH resources, the gNB initiatesthe beam failure recovery procedure. As part of this procedure, the gNBtransmits (S13—FIG. 3) a physical downlink control channel, PDCCH,downlink control information, DCI, with an uplink grant. DCIs on thePDCCH also include a cyclic redundancy check, CRC field which isscrambled with a radio network temporary identifier, RNTI, of the UE.Thereby, the UE can detect, whether or not the gNB has intended the DCIfor the UE to be used in the beam failure recovery procedure.

Assuming the UE has received an uplink grant, the mobile terminal 110transmits (S14—FIG. 3) in form of an uplink MAC control element a beamfailure recover request to the gNB. This request includes at least oneof the following: an explicit or implicit information about identifyingthe UE and new downlink beam candidate information for the gNB; anexplicit or implicit information about identifying the UE and whether ornot new downlink beam candidates exist.

Finally, in response to the beam failure recovery request, the gNBtransmits (S15—FIG. 3) a beam failure recovery response to the UE inform of a PDCCH DCI including a confirmation, for example, anacknowledgement. This response is a response to the beam failurerecovery request transmitted by the UE before. In particular, only afterthis response has been received by the UE, it knows that the informationindicating new downlink beam candidates has been successfully received,and has been put into practice.

Alternatively, when the mobile terminal has not suggested any newdownlink beam candidate, the gNB may include information on the newdownlink beam in the beam failure recovery response to the UE. Dependingon the number of potentially available downlink beam, this informationmay still be accommodated in a response in form of a PDCCH DCI. Alsothen can both the gNB and the UE revert to the same pair of the newdownlink and the current uplink (serving) beam, thereby successfullycompleting the beam failure recovery procedure.

FIG. 4 now assumes another 3GPP NR deployment scenario. In more detail,this figure depicts the initiation of beam failure recovery procedure inthe context of a 2-step beam failure recovery procedure, where the UEand the gNB communicate over a pair of downlink and uplink (serving)beams. Also here downlink and uplink (serving) beams are one of aplurality of downlink beams and one of a pair of uplink beams that canbe configured by the gNB to the UE. Notably, the 2-step beam failurerecovery procedure is restricted to dedicated uplink radio resourcesfrom the physical uplink control channel, PUCCH only.

This procedure is very similar to the 4-step beam failure recoveryprocedure shown in the previous figure. The transmissions between the UEand the gNB for the allocation of the dedicated uplink resources(S21—FIG. 4) and the transmission of the beam failure recovery response(S23—FIG. 4) correspond to the respective steps in the previousprocedure. Moreover, the only difference resides in the format of thebeam failure recovery signal (S22—FIG. 4).

Here, use is made of the fact that an uplink control information, UCI,on the PUCCH depending on the given format can include a sufficientnumber of bits, for example 1 or 2 bits in PUCCH format 1a/1b, 20 codedbits in PUCCH format 2/2a/2b, or even 48 coded bits in PUCCH format 3.

Thus, it is suggested in this example that the UE transmits as beamfailure recovery signal to the gNB not only an UCI of PUCCH, whichresembles a dedicated uplink radio resource, but also carries theinformation of the beam failure recovery request, namely at least one ofthe following: an explicit or implicit information about identifying theUE and new downlink beam candidate information for the gNB; an explicitor implicit information about identifying the UE and whether or not newdownlink beam candidates exist.

Robust Allocation Mechanism As discussed before, the present disclosurefocuses on a robust mechanism that enables the base station to respondto the detection of a downlink beam failure event while reducing theamount of uplink radio resources that are blocked (assigned) forinitiating the beam failure recovery procedure. The reduction of theamount of uplink radio resources, however, requires the base station, inone example, to carefully select the dedicated uplink radio resources tobe assigned.

For this purpose, the base station may determine the subset from amongall potentially available uplink beams based on most recent qualityand/or power measurements. In this context, it may be advantageous torevert to reference signals that are signaled either on all potentiallyavailable downlink beams or the uplink beams. From this, the basestation can then select the subset with reference to the measuredquality and/or power values.

Assuming an 3GPP NR deployment scenario, the base station may revert,for the determination of the subset of uplink beams, to all potentiallyavailable uplink reference signals, preferably sounding referencesignals, SRS that are transmitted by mobile terminals on all potentiallyavailable or at least on the most relevant uplink beams.

The base station may also revert, for this determination of the subsetof uplink beams, to reports, preferably to channel status information,CSI, reports that are drawn up by a mobile terminal on measurements ofdownlink reference signals, preferably, CSI-RS, having been transmittedby the base station on all potentially available downlink beams.

Either way, it can be ensured that the subset of the uplink resourcesfits the purpose of allowing the mobile terminal to robustly respond tothe detection of a downlink beam failure event, namely without riskingthat the beam failure recovery signal cannot be received by the basestation.

Mobility State

In an exemplary implementation, the focus laid on an efficient mechanismfor allocating the dedicated uplink radio resources on the subset ofuplink beams. To achieve this, the base station varies the number ofuplink beams that form the subset on which dedicated uplink radioresources are allocated to the mobile terminal. Particularly, by varyingthe number of uplink beams, the base station strives to account forvarying (actual) situations (e.g., low or high number of positionchanges) in the mobile terminal.

As seen from the discussion above, one of the main causes of beamfailures is the mobility (i.e., varying spatial position) of the mobileterminal. Should the mobile terminal change its position at a high rate,it is difficult to predict for the bases station which the mostpertinent dedicated uplink radio resource will be, should there occur adownlink beam failure. In other words, a highly changing position ofmobile terminals makes it difficult for the base station to allocatededicated uplink radio resources on a subset of uplink beams which stillmeet the requirements of a reliable beam failure recovery procedure.

With these difficulties in mind, the present disclosure proposes thebase station to maintain a mobility state for each mobile terminal. Themobility state distinguishes, for each mobile terminal between a lownumber and a high number of positional changes in a given time period.In other words, based on the mobility state, the base station canascertain for each mobile terminal if positional changes have occurred(in the past) at a low rate or a high rate.

This mobility state is then used by the base station to predict thenumber of uplink beams in the subset to ensure a reliable beam failurerecover procedure. Thus, the number of uplink beams forming the subsetof all potentially available uplink beams may be determined by the basestation corresponding to the mobility state of the respective mobileterminal.

In one example, namely for a mobile terminal with a mobility statecorresponding to a low positional change rate, the base station mayvalidly predict that the mobile terminal's position will also not oftenchange in the future, hence, the it suffices to allocate dedicateduplink radio resources on a low number of uplink beams (for example oneor two uplink beams). In a different example, namely for a mobileterminal with a mobility state corresponding to a high positional changerate, the base station may, in contrast, validly predict that the mobileterminal's position will also often change in the future, hence itbecomes necessary to allocate dedicated uplink radio resources on a highnumber of uplink beams (for example three or more).

Exemplarily, the mobility state, thus the positional change rate, can bedetermined by both the base station and the mobile terminal based on thenumber of reconfiguration commands for the downlink beam (beemsteering)that are transmitted from the base station to the mobile terminal.Despite the fact that the reconfiguration of the downlink beam iseffected at the base station, the mobile terminal will take accountthereof in form of a reconfiguration command, namely which instructs themobile terminal to reconfigure its beam pair to include a new downlinkbeam.

Also exemplarily, the mobility state, thus the positional change rate,can be determined based on the number positional changes, which ispreferably determined from positioning measurements in the mobileterminal for a given time period and then signaled to the base station.In other words, the mobile terminal itself determines its positionalchange rate, for instance by performing positioning measurementsincluding checking for new downlink beams, and then signals same to thebase station.

In both cases, the mobility state facilitates the selection of asufficient number of uplink beams for the mobile terminal to robustlyrespond to the detection of a downlink beam failure event, namelywithout risking that the beam failure recovery signal cannot be receivedby the base station.

Up-to-Datedness of Allocation

In another exemplary implementation, the focus is again laid on anefficient mechanism for allocating the dedicated uplink radio resourceson the subset of uplink radio beams. To achieve this, each allocation ofdedicated uplink radio resources to a mobile terminal has an expirationtime. Thereby, the up-to-datedness of allocations of dedicated uplinkradio resources can be ensured, as well as the fact that the resourcesare only blocked for a limited amount of time.

As apparent from the discussion above, the base station allocatingdedicated uplink radio resources to a mobile station cannot always copewith varying (actual) situations (e.g., position changes) in the mobileterminal. An allocation on one subset of uplink beams may be valid for amobile terminal in one position, however not for the same mobileterminal after moving to another position.

Thus, the present disclosure proposes that each allocation is valid fora given (short) period of time, and exceptionally only until a new(re-)allocation is received. In other words, irrespective of whether themobile station receives from the base station an exclusive ornon-exclusive allocation of dedicated uplink resources for the beamfailure recovery procedure, these resources are only blocked for alimited amount of time.

This can be ensured by base station 160 when transmitting (cf. S01—FIG.2) the allocation to the mobile station 110, also indicating a timeperiod for which dedicated uplink radio resources are valid. Forexample, together with the allocation of the dedicated uplink radioresources, both the base station and the mobile terminal can initiate acountdown timer. Once this timer has expired, the base station as wellas the mobile terminal knows that the dedicated uplink radio resourcescan no longer be used, are hence not blocked anymore.

However, to avoid cases no or only an expired allocation, the mobileterminal may transmit to the base station an indication for the basestation to (re-)initiate allocation of dedicated uplink radio resourcesfor the beam failure recovery procedure.

Assuming an NR deployment scenario, the indication for (re-)initiateallocation of the dedicated uplink radio resources is (implicit) achannel status information, CSI, report, signaling a quality or power ofthe serving downlink beam below a given threshold value, or a dedicatedtransmission, preferably in form of either a RRC message, or an uplinkMAC CE, signaling an explicit request for (re-)initiating allocation ofthe dedicated uplink radio resources.

In summary, the expiration of an allocation of dedicated uplink radioresources further improves the efficient usage of same resources. Notonly does the expiration of an allocation of resources facilitates anup-to-datedness which is anyway necessary for the allocation to reflectthe actual (current) situation of the mobile station, it also preventsfrom an blockage of resources, which is particular advantageous for thecase where same resources are allocated in an exclusive manner.

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of each embodiment described above can be partly or entirelyrealized by an LSI such as an integrated circuit, and each processdescribed in the each embodiment may be controlled partly or entirely bythe same LSI or a combination of LSIs. The LSI may be individuallyformed as chips, or one chip may be formed so as to include a part orall of the functional blocks. The LSI may include a data input andoutput coupled thereto. The LSI here may be referred to as an IC, asystem LSI, a super LSI, or an ultra LSI depending on a difference inthe degree of integration. However, the technique of implementing anintegrated circuit is not limited to the LSI and may be realized byusing a dedicated circuit, a general-purpose processor, or aspecial-purpose processor. In addition, a FPGA (Field Programmable GateArray) that can be programmed after the manufacture of the LSI or areconfigurable processor in which the connections and the settings ofcircuit cells disposed inside the LSI can be reconfigured may be used.The present disclosure can be realized as digital processing or analogueprocessing. If future integrated circuit technology replaces LSIs as aresult of the advancement of semiconductor technology or otherderivative technology, the functional blocks could be integrated usingthe future integrated circuit technology. Biotechnology can also beapplied.

According to a first aspect, a mobile terminal is suggested forcommunicating in a mobile communication system with a base station usingat least one of a plurality of downlink beams and at least one of aplurality of uplink beams, each of the downlink and uplink beams havingdifferent directivities and/or coverage, comprising: which, inoperation, receives for a beam failure recovery, BFR, procedure anallocation of dedicated uplink radio resources for transmitting a beamfailure recovery signal, a processor which, in operation, detects adownlink beam failure event and, in response thereto, initiates the beamfailure recovery procedure, including the transceiver transmitting thebeam failure recovery signal using the dedicated uplink radio resourcesfrom the allocation; wherein the dedicated uplink radio resources arerestricting the transmission to a subset of the plurality of uplinkbeams that can be exclusively allocated by the base station to themobile terminal.

According to a second aspect, which can be combined with the firstaspect, the subset of the plurality of the uplink beams is exclusivelyallocated to the mobile terminal based on: uplink reference signals,preferably sounding reference signals, SRS, transmitted by the mobileterminal on the plurality of uplink beams, or a report, preferably achannel status information, CSI, report, by the mobile terminal onmeasurements of downlink references signals, preferably CSI-RSs,transmitted by the base station on the plurality of downlink beams.

According to a third aspect, which can be combined with the first orsecond aspect, the number of uplink beams forming the subset of theplurality of uplink beams corresponds to one, two or three uplink beams.

According to a fourth aspect, which can be combined with one of thefirst to third aspects, the number of uplink beams forming the subset ofthe plurality of uplink beams corresponds to a mobility state of themobile terminal that distinguishes between a low and a high rate ofpositional changes of the mobile terminal.

According to a fifth aspect, which can be combined with the fourthaspect, the mobility state of the mobile terminal is determined basedon, the number of reconfiguration commands for the downlink beam thatare transmitted by the base station to the mobile terminal for a timeperiod, or the number positional changes, preferably determined frompositioning measurements, in the mobile terminals for a time period andsignaled to the base station.

According to a sixth aspect, which can be combined with one of the firstto fifth aspect, the transceiver, in operation, additionally receivesfor the beam failure recovery procedure an indication indicating thenumber of uplink beams in the subset of the plurality of uplink beamsthat is to be used in the beam failure recovery procedure.

According to a seventh aspect, which can be combined with one of thefirst to sixth aspect, the indication indicating the number of uplinkbeams in the subset of the plurality of uplink beams is to be used isreceived in: an radio resource configuration, RRC, message, or a mediumaccess control, MAC, control element, CE, or a downlink controlinformation, DCI.

According to a eighth aspect, another mobile terminal is proposed forcommunicating in a mobile communication system with a base station usingat least one of a plurality of downlink beams and at least one of aplurality of uplink beams, each of the downlink and uplink beams havingdifferent directivities, comprising: which, in operation, receives for abeam failure recovery, BFR, procedure an allocation of dedicated uplinkradio resources for transmitting a beam failure recovery signal, aprocessor which, in operation, detects a downlink beam failure eventand, in response thereto, initiates the beam failure recovery procedure,including the transceiver transmitting the beam failure recovery signalusing the dedicated uplink radio resources of the previous allocation;wherein the dedicated uplink radio resources are restricting thetransmission to a subset of the plurality of uplink beams that can benon-exclusively allocated by the base station to the mobile terminal.

According to a ninth aspect, which can be combined with the eighthaspect, the transmission on the subset of the plurality of uplink beams,to which the beam failure recovery signal on the dedicated uplink radioresources is restricted, enables the base station to identify the mobileterminal.

According to a tenth aspect, which can be combined with the eighth orninth aspect, in case the dedicated uplink radio resources include aphysical uplink control channel, PUCCH, the transmission of demodulationreference signals, DM-RS together with the beam failure recovery signalin the PUCCH enables the base station to identify the mobile terminal.

According to an eleventh aspect, which can be combined with one of theeighth to tenth aspect, the allocation of dedicated uplink radioresources includes an instruction for the mobile terminal to include itsidentification in subsequent messages of the beam failure recoveryprocedure.

According to a twelfth aspect, which can be combined with one of thefirst to eleventh aspect, the dedicated uplink radio resourcescorrespond to one of: a contention-free resource, preferably acontention-free preamble sequence with a time and frequency reference,of a physical random access channel, PRACH, and a contention-freeresource, preferably uplink control information, UCI with a time andfrequency reference, of a physical uplink control channel, PUCCH.

According to a thirteenth aspect, which can be combined with one of thefirst to twelfth aspect, the allocation of the dedicated uplink radioresources is received via one of: a radio resource configuration, RRC,connection reconfiguration or RRC connection setup message, a downlinkmedium access control, MAC, control element, CE, a downlink controlinformation, DCI, and a control protocol data unit, PDU of a packet dataconvergence protocol, PDCP.

According to a fourteenth aspect, which can be combined with one of thefirst to twelfth aspect, the allocation of the dedicated uplink radioresource includes that the transceiver, in operation, receives: aconfiguration of the dedicated uplink radio resource via an RRCconnection setup or reconfiguration message, and an activation for thededicated uplink radio resources from the configuration via one of MACCE, a DCI, and a PDCP control PDU.

According to a fifteenth aspect, which can be combined with one of thefirst to fourteenth aspect, the allocation of dedicated uplink resourcesis valid either for a time period, or until a new allocation isreceived.

According to a sixteenth aspect, which can be combined with one of thefifteenth aspect, the time period for which the allocation of dedicateduplink resources is valid is indicated in the allocation.

According to a seventeenth aspect, which can be combined with one of thefirst to sixteenth aspect, the transceiver, in operation, transmits anindication for the base station to (re-)initiate allocation of dedicateduplink radio resources for the beam failure recovery procedure.

According to a eighteenth aspect, which can be combined with theseventeenth aspect, the indication for (re-)initiating allocation of thededicated uplink radio resources is: a channel status information, CSI,report, signaling a quality or power of the serving downlink beam belowa threshold value, or a dedicated transmission, preferably in form ofeither a RRC message, or an uplink MAC CE, signaling an explicit requestfor (re-) initiating allocation of the dedicated uplink radio resources.

According to a nineteenth aspect, a method for initiating a beam failurerecovery procedure is suggested to be performed by a mobile terminalconfigured to communicate in a mobile communication system with a basestation using at least one of a plurality of downlink beams and at leastone of a plurality of uplink beams, each of the downlink and uplinkbeams having different directivities and/or coverage, the methodcomprising the steps of: for a beam failure recovery, BFR, procedure anallocation of dedicated uplink radio resources for transmitting a beamfailure recovery signal, detecting a downlink beam failure event and, inresponse thereto, initiating the beam failure recovery procedure,including transmitting the beam failure recovery signal using thededicated uplink radio resources from the allocation; wherein thededicated uplink radio resources are restricting the transmission to asubset of the plurality of uplink beams that can be exclusivelyallocated by the base station to the mobile terminal.

According to a twentieth aspect, which can be combined with thenineteenth aspect, the subset of the plurality of the uplink beams isexclusively allocated to the mobile terminal based on: uplink referencesignals, preferably sounding reference signals, SRS, transmitted by themobile terminal on the plurality of uplink beams, or a report,preferably a channel status information, CSI, report, by the mobileterminal on measurements of downlink references signals, preferablyCSI-RSs, transmitted by the base station on the plurality of downlinkbeams.

According to a twenty-first aspect, which can be combined with thenineteenth or twentieth aspect, the number of uplink beams forming thesubset of the plurality of uplink beams corresponds to one, two or threeuplink beams.

According to a twenty-second aspect, which can be combined with one ofthe nineteenth to twenty first aspect, the number of uplink beamsforming the subset of the plurality of uplink beams corresponds to amobility state of the mobile terminal that distinguishes between a lowand a high rate of positional changes of the mobile terminal.

According to a twenty-third aspect, which can be combined with one ofthe nineteenth to twenty second aspect, the mobility state of the mobileterminal is determined based on, the number of reconfiguration commandsfor the downlink beam that are transmitted by the base station to themobile terminal for a time period, or the number positional changes,preferably determined from positioning measurements, in the mobileterminals for a time period and signaled to the base station.

According to a twenty-fourth aspect, which can be combined with one ofthe nineteenth to twenty third aspect, the method comprises the step of:additionally receiving for the beam failure recovery procedure anindication indicating the number of uplink beams in the subset of theplurality of uplink beams that is to be used in the beam failurerecovery procedure.

According to a twenty-fifth aspect, which can be combined with twentyfourth aspect, the indication indicating the number of uplink beams inthe subset of the plurality of uplink beams is to be used is receivedin: an radio resource configuration, RRC, message, or a medium accesscontrol, MAC, control element, CE, or a downlink control information,DCI.

According to a twenty-sixth aspect, another method for initiating a beamfailure recovery procedure is suggested to be performed by a mobileterminal configured to communicate with a base station using at leastone of a plurality of downlink beams and at least one of a plurality ofuplink beams, each of the uplink and downlink beams having differentdirectivities, comprising: receiving for a beam failure recovery, BFR,procedure an allocation of dedicated uplink radio resources for a beamfailure recovery signal, detecting a downlink beam failure event and, inresponse thereto, initiating the beam failure recovery procedure,including transmitting the beam failure recovery signal using thededicated uplink radio resources of the previous allocation; wherein thededicated uplink radio resources are restricting the transmission to asubset of the plurality of uplink beams that can be non-exclusivelyallocated by the base station to the mobile terminal.

According to a twenty-seventh aspect, which can be combined with thetwenty sixth aspect, the transmission on the subset of the plurality ofuplink beams, to which the beam failure recovery signal on the dedicateduplink radio resources is restricted, enables the base station toidentify the mobile terminal.

According to a twenty-eighth aspect, which can be combined with thetwenty sixth or twenty seventh aspect, in case the dedicated uplinkradio resources include a physical uplink control channel, PUCCH, thetransmission of demodulation reference signals, DM-RS together with thebeam failure recovery signal in the PUCCH enables the base station toidentify the mobile terminal.

According to a twenty-ninth aspect, which can be combined with one ofthe twenty sixth to twenty eighth aspect, the allocation of dedicateduplink radio resources includes an instruction for the mobile terminalto include its identification in subsequent messages of the beam failurerecovery procedure.

According to a thirtieth aspect which can be combined with one of thenineteenth to twenty ninth aspect, the dedicated uplink radio resourcescorrespond to one of: a contention-free resource, preferably uplinkcontrol information, UCI with a time and frequency reference, of aphysical uplink control channel, PUCCH.

According to a thirty-first aspect, which can be combined with one ofthe nineteenth to thirtieth aspect, the allocation of the dedicateduplink radio resources is received via one of: a radio resourceconfiguration, RRC, connection reconfiguration or RRC connection setupmessage, downlink medium access control, MAC, control element, CE, adownlink control information, DCI, and a control protocol data unit,PDU, of a packet data convergence protocol, PDCP.

According to a thirty-second aspect, which can be combined with one ofthe nineteenth to thirtieth aspect, the allocation of the dedicateduplink radio resource includes receiving: a configuration of thededicated uplink radio resource via an RRC connection establishment orreconfiguration message, and an activation for the dedicated uplinkradio resources from the configuration via one of MAC CE, a DCI, and aPDCP control PDU.

According to the thirty-third aspect, which can be combined with one ofthe nineteenth to thirty second aspect, the allocation of dedicateduplink resources is valid either for a time period, or until a newallocation is received.

According to the thirty-fourth aspect, which can be combined with thethirty third aspect, the time period for which the allocation ofdedicated uplink resources is valid is indicated in the allocation.

According to the thirty-fifth aspect, which can be combined with one ofthe nineteenth to thirty-fourth aspect, the method comprises the stepof: transmitting an indication for the base station to (re-)initiateallocation of dedicated uplink radio resources for the beam failurerecovery procedure.

According to the thirty-sixth aspect, which can be combined with thethirty fifth aspect, the indication for (re-)initiating allocation ofthe dedicated uplink radio resources is: a channel status information,CSI, report, signaling a quality or power of the serving downlink beambelow a threshold value, or a dedicated transmission, preferably in formof either a RRC message, or an uplink MAC CE, signaling an explicitrequest for (re-) initiating allocation of the dedicated uplink radioresources.

According to the thirty-seventh aspect, a base station is suggested forcommunicating in a mobile communication system with a mobile terminalusing at least one of a plurality of downlink beams and at least one ofa plurality of uplink beams, each of the downlink and uplink beamshaving different directivities and/or coverage, comprising: a processorwhich, in operation, performs the beam failure recovery procedure,including the transceiver receiving from the mobile terminal the beamfailure recovery signal using the dedicated uplink radio resources fromthe allocation; wherein the dedicated uplink radio resources arerestricting the transmission to a subset of the plurality of uplinkbeams that can be exclusively allocated by the base station to themobile terminal.

According to a thirty-eighth aspect, another base station is proposedfor communicating in a mobile communication system with a mobileterminal using at least one of a plurality of downlink beams and atleast one of a plurality of uplink beams, each of the downlink anduplink beams having different directivities and/or coverage, comprising:a processor which, in operation, imitates the beam failure recoveryprocedure, including the transceiver receiving from the mobile terminalthe beam failure recovery signal using the dedicated uplink radioresources from the allocation; wherein the dedicated uplink radioresources are restricting the transmission to a subset of the pluralityof uplink beams that can be non-exclusively allocated by the basestation to the mobile terminal.

According to a thirty-ninth aspect, a method for initiating a beamfailure recovery procedure is suggested to be performed by a basestation configured to communicate in a mobile communication system witha mobile terminal using at least one of a plurality of downlink beamsand at least one of a plurality of uplink beams, each of the downlinkand uplink beams having different directivities and/or coverage, themethod comprising the steps of: initiating the beam failure recoveryprocedure, in response to receiving from the mobile terminal the beamfailure recovery signal using the dedicated uplink radio resources fromthe allocation; wherein the dedicated uplink radio resources arerestricting the transmission to a subset of the plurality of uplinkbeams that can be exclusively allocated by the base station to themobile terminal.

According to a fortieth aspect, another method for initiating a beamfailure recovery procedure is proposed to be performed by a base stationconfigured to communicate in a mobile communication system with a mobileterminal using at least one of a plurality of downlink beams and atleast one of a plurality of uplink beams, each of the downlink anduplink beams having different directivities and/or coverage, the methodcomprising the steps of: initiating the beam failure recovery procedure,in response to receiving from the mobile terminal the beam failurerecovery signal using the dedicated uplink radio resources from theallocation; wherein the dedicated uplink radio resources are restrictingthe transmission to a subset of the plurality of uplink beams that canbe non-exclusively allocated by the base station to the mobile terminal.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A user equipment, comprising: a transceiver which, in operation,receives a configuration of dedicated uplink radio resources; and aprocessor which, in response to detecting a downlink beam failure event,initiates a beam failure recovery procedure (BFR) including thetransceiver transmitting a beam failure recovery signal using thededicated uplink radio resources pursuant to the configuration, whereinthe configuration includes a timer indicating a validity time of thededicated uplink radio resources, wherein the validity time of the timeris differently defined from a time length of the dedicated uplink radioresources.
 2. The user equipment according to claim 1, wherein a subsetof a plurality of uplink beams is dedicatedly allocated to the userequipment based on at least one of: uplink reference signals (RS) orsounding reference signals (SRS) transmitted by the user equipment onthe plurality of uplink beams; and a report or a channel statusinformation (CSI) report, by the user equipment, on measurements ofdownlink references signals or CSI-RSs, transmitted by a base station ona plurality of downlink beams.
 3. The user equipment according to claim2, wherein a number of the uplink beams forming the subset correspondsto one, two or three uplink beams.
 4. The user equipment according toclaim 2, wherein 1 number of the uplink beams forming the subsetcorresponds to a mobility state of the user equipment that distinguishesbetween a low and a high rate of positional changes of the userequipment.
 5. The user equipment according to claim 4, wherein themobility state of the user equipment is determined based on at least oneof: a number of reconfiguration commands for the downlink beam that aretransmitted by a base station to the user equipment for a first timeperiod; and a number of positional changes, determined from positioningmeasurements, in the user equipment for a second time period andsignaled to the base station.
 6. The user equipment according to claim1, wherein the transceiver, in operation, additionally receives for thebeam failure recovery procedure (BFR) an indication indicating a numberof uplink beams in a subset of a plurality of uplink beams that is to beused in the beam failure recovery procedure (BFR).
 7. The user equipmentaccording to claim 6, wherein the indication is received in at least oneof: a radio resource configuration (RRC) message; a medium accesscontrol (MAC) control element (CE); and a downlink control information(DCI).
 8. The user equipment according to claim 1, wherein the dedicateduplink radio resources correspond to one of: a contention-free resource,comprising a contention-free preamble sequence with a time and frequencyreference, of a physical random access channel (PRACH); and acontention-free resource, comprising uplink control information (UCI)with a time and frequency reference, of a physical uplink controlchannel (PUCCH), and/or wherein the configuration of the dedicateduplink radio resources is received via one of: a radio resourceconfiguration (RRC) connection reconfiguration or RRC connection setupmessage; a downlink medium access control (MAC) control element (CE); adownlink control information (DCI); and a control protocol data unit(PDU) of a packed data convergence protocol (PDCP).
 9. The userequipment according to claim 1, wherein the transceiver, in operation,receives: the configuration of the dedicated uplink radio resources viaone of a radio resource configuration (RRC) connection setup message anda RRC reconfiguration message; and an activation for the dedicateduplink radio resources via one of a medium access control (MAC) controlelement (CE), a downlink control information (DCI), and a packet dataconvergence protocol (PDCP) control protocol data unit (PDU).
 10. Theuser equipment according to claim 1, wherein the transceiver, inoperation, transmits an indication for a base station to initiate theconfiguration of the dedicated uplink radio resources, wherein theindication for initiating the configuration is at least one of: achannel status information (CSI) report, signaling a quality or power ofa serving downlink beam below a threshold value; and a dedicatedtransmission, in form of either a radio resource control (RRC) message,or an uplink medium access control (MAC) control element (CE), signalingan explicit request for initiating the configuration of the dedicateduplink radio resources.
 11. The user equipment according to claim 1,wherein the dedicated uplink radio resources restrict transmission fromthe user equipment to a subset of a plurality of uplink beams that canbe dedicatedly allocated by a base station to the user equipment.
 12. Amethod performed by a user equipment, comprising: receiving aconfiguration of dedicated uplink radio resources; and in response todetecting a downlink beam failure event, initiating a beam failurerecovery procedure (BFR) including transmitting a beam failure recoverysignal using the dedicated uplink radio resources pursuant to theconfiguration, wherein the configuration includes a timer indicating avalidity time of the dedicated uplink radio resources, wherein thevalidity time of the timer is differently defined from a time length ofthe dedicated uplink radio resources.
 13. The method according to claim12, wherein the dedicated uplink radio resources restrict transmissionfrom the user equipment to a subset of a plurality of uplink beams thatcan be dedicatedly allocated by a base station to the user equipment.